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Marge Bot pushed to branch master at Glasgow Haskell Compiler / GHC

Commits:

ca5b0283

by Sergey Vinokurov at 2025-09-01T23:02:23-04:00

Remove unnecessary irrefutable patterns from Bifunctor instances for tuples

Implementation of https://github.com/haskell/core-libraries-committee/issues/339

Metric Decrease:
    mhu-perf

2 changed files:

libraries/base/changelog.md
libraries/base/src/Data/Bifunctor.hs

Changes:

libraries/base/changelog.md

@@ -7,6 +7,7 @@
    * Modify the implementation of `Data.List.sortOn` to use `(>)` instead of `compare`. ([CLC proposal #332](https://github.com/haskell/core-libraries-committee/issues/332))
    * `GHC.Exts.IOPort#` and its related operations have been removed  ([CLC #213](https://github.com/haskell/core-libraries-committee/issues/213))
    * Fix bug where `naturalAndNot` was incorrectly truncating results ([CLC proposal #350](github.com/haskell/core-libraries-committee/issues/350))
 +  * Remove extra laziness from `Data.Bifunctor.Bifunctor` instances for all tuples to have the same laziness as their `Data.Functor.Functor` counterparts (i.e. they became more strict than before) ([CLC proposal #339](https://github.com/haskell/core-libraries-committee/issues/339))
  ## 4.22.0.0 *TBA*
    * Shipped with GHC 9.14.1

libraries/base/src/Data/Bifunctor.hs

@@ -133,39 +133,39 @@ class (forall a. Functor (p a)) => Bifunctor p where
      second = bimap id
 --- | Class laws for tuples hold only up to laziness. Both
 --- 'first' 'id' and 'second' 'id' are lazier than 'id' (and 'fmap' 'id'):
 +-- | Tuple instances have the same laziness as for 'Functor'. Both
 +-- 'first' 'id' and 'second' 'id' have the same laziness as 'id' (and 'fmap' 'id'):
  --
 --- >>> first id (undefined :: (Int, Word)) `seq` ()
 --- ()
 --- >>> second id (undefined :: (Int, Word)) `seq` ()
 --- ()
 +-- >>> first id (errorWithoutStackTrace "error!" :: (Int, Word)) `seq` ()
 +-- *** Exception: error!
 +-- >>> second id (errorWithoutStackTrace "error!" :: (Int, Word)) `seq` ()
 +-- *** Exception: error!
  -- >>> id (errorWithoutStackTrace "error!" :: (Int, Word)) `seq` ()
  -- *** Exception: error!
  --
  -- @since 4.8.0.0
  instance Bifunctor (,) where
 -    bimap f g ~(a, b) = (f a, g b)
 +    bimap f g (a, b) = (f a, g b)
  -- | @since 4.8.0.0
  instance Bifunctor ((,,) x1) where
 -    bimap f g ~(x1, a, b) = (x1, f a, g b)
 +    bimap f g (x1, a, b) = (x1, f a, g b)
  -- | @since 4.8.0.0
  instance Bifunctor ((,,,) x1 x2) where
 -    bimap f g ~(x1, x2, a, b) = (x1, x2, f a, g b)
 +    bimap f g (x1, x2, a, b) = (x1, x2, f a, g b)
  -- | @since 4.8.0.0
  instance Bifunctor ((,,,,) x1 x2 x3) where
 -    bimap f g ~(x1, x2, x3, a, b) = (x1, x2, x3, f a, g b)
 +    bimap f g (x1, x2, x3, a, b) = (x1, x2, x3, f a, g b)
  -- | @since 4.8.0.0
  instance Bifunctor ((,,,,,) x1 x2 x3 x4) where
 -    bimap f g ~(x1, x2, x3, x4, a, b) = (x1, x2, x3, x4, f a, g b)
 +    bimap f g (x1, x2, x3, x4, a, b) = (x1, x2, x3, x4, f a, g b)
  -- | @since 4.8.0.0
  instance Bifunctor ((,,,,,,) x1 x2 x3 x4 x5) where
 -    bimap f g ~(x1, x2, x3, x4, x5, a, b) = (x1, x2, x3, x4, x5, f a, g b)
 +    bimap f g (x1, x2, x3, x4, x5, a, b) = (x1, x2, x3, x4, x5, f a, g b)
  -- | @since 4.8.0.0